1. Field of the Invention
The present invention relates to an inner cutter unit for an electric rotary shaver and more particularly to an inner cutter unit in which an inner cutter body is integrally provided on an inner cutter base that is rotated by a motor of the shaver.
2. Prior Art
In an electric rotary shaver, a shaver head frame is detachably disposed on the upper portion of the main body case of the shaver. The shaver head frame includes an outer cutter unit and an inner cutter unit; and the main body case is, in addition to other components, equipped with a driving source (motor), a driving mechanism, a power supply and an operating switch.
The rotary shaft (or the axle) of the motor extends from the main body case into the shaver head frame and engages with the inner cutter unit. Some shavers include only one inner cutter unit, and other shavers involve a plurality of (three, for instance) inner cutter units.
One example of the inner cutter unit of an electric rotary shaver is shown in FIGS. 6 and 7.
The external shape of the inside circumferential cutter blades 55 and outside circumferential cutter blades 56 is formed by punching out a metal plate which is, for instance, a stainless steel plate; and hole working is performed in the base section 51 so as to form an engagement hole 54 therein that engages with the shaft portion 53 of an inner cutter base 52. Circumferential edge portion of the base section 51 is subjected to bending, so that a plurality of inner cutter bodies 57, in which the inside circumferential cutter blades 55 and the outside circumferential cutter blades 56 form pairs, are formed in an upright posture with respect to the base section 51. The inner cutter bodies 57 are bent so as to be inclined in the direction of rotation (the clockwise direction in FIG. 6). The shaft portion 53 of the inner cutter base 52 is brought into an engagement with the engagement hole 54 of the base section 51 that has thereon the inner cutter bodies 57, thus forming an integral inner cutter unit 58. The inner cutter unit 58 is rotationally driven with a bearing portion (not shown) formed on the undersurface side of the shaft portion 53 being engaged with an axle of the motor (not shown) of the shaver.
Since the inner cutter bodies 57 are obtained by punching and bending a metal plate by press working, a space such as a bending margin, etc., that is required for bending is necessary in order to form the inner cutter bodies 57 that have a specified area within a fixed circumference. Accordingly, there are limits to the number of inside circumferential cutter blades 55 and outside circumferential cutter blades 56; and as a result, there are also limits to how far the efficiency can be improved when hair is cut (or shaved) using such an electric rotary shaver.
Furthermore, since the tip end (cutter blade surfaces 59) of the inside circumferential cutter blades 55 and outside circumferential cutter blades 56 generate dimensional differences t in the radial direction, as seen from FIG. 8, that is caused by shear droop. As a result, the amount of area of one tip end (cutter blade surface 59), which makes a sliding contact with outer cutter, would become different from that of another tip end (cutter blade surface 59), causing a friction increase and an efficiency drop.
Furthermore, the inner cutter bodies 57 shown in FIG. 7, in which the inside circumferential cutter blades 55 and outside circumferential cutter blades 56 are formed continuously into an integral unit, are formed so as to rise from the base section 51 by bending and then bent so as to incline in the direction of rotation of the inner cutter unit 58. In some cases, therefore, the rotational trajectory drawn by the cutter blade surface 59 and shown in FIG. 9 becomes wider than the width dimension thereof. In other words, in some cases, the cutter blade surface 59 draws (during the rotation) a trajectory regulated by the inside circumferential edge portion 59a and the outside circumferential edge portion 59b; as a result, it becomes difficult to obtain precision in the rotational radius, and the element that draws the rotational trajectory needs to be set at larger values.